Question

Show with an activity that sound cannot travel through vaccume.

Answer 1

An electric bell and a glass belljar was used, as shown in figure given above. The bell was hung inside the belljar and it eas connected to a vaccum pump. On pressing the bell switch, its sound was heard. When the air inside the jar was slowly pumped out using the vaccum pump the sound get lower, even though the same amount of electric current was passed through it. When the complete air inside the bell jar was pumped out, no sound could be heard.

The conclusion made through this experiment was that sound cannot travel in vaccum and hence we always need some medium to hear sound.

Sound waves do not travel in vaccum because there are no particles present in vaccum for compression and rarefaction.

Answer 2

Take an air tight glass bell jar and suspend an electric bell inside it. Connect the jar from a suction pump.
Press the key to switch on electric circuit. What do u observe? u hear a sound from bell. Now remove the air from the jar with the help of suction pumps. What do u observe now. Loudness of sound become decrease and finally become 0. No sound is heard from bell. It means that bell is producing sound but we cannot hear it due to absence of air between bell and wall of jar.